(a) Field of the Invention:
The present invention relates to a photographing indication device for microscopes.
(b) Description of the Prior Art:
For general photographing with a microscope, it is already known that an indication member having indication lines such as cross lines, double cross lines or a frame indicating a photographing range, can be arranged in the observation optical path at a position corresponding to the image surface of a photographing device, so as to permit accurate focusing or facilitate determination of composition.
Conventionally, the above-mentioned indication lines were composed by stretching piano wires at the required position, or engraving said lines or evaporating chromium on one side of said transparent plate-shaped indication member so as to be clearly observable as dark lines without being mixed with an image to be observed within the visual field during microscopy under the bright field illumination, thereby assuring sufficient brightness within the visual field including said image and background thereof. However, during microscopy under the dark field illumination or reflecting fluorescence illumination, for example, for observing images which are often formed as small bright points scattered against dark background, these indication lines were observable only at areas overlapped with the small images and were invisible against dark background, thereby being practically useless as such.
For this reason, Japanese Patent Publication No. 16580/1963, for example, discloses a composition wherein an indication member having an opaque plate-shaped surface and transparent indication lines is illuminated with a small lamp arranged on the outer circumference thereof. However, illumination is still dark at the position on the opposite side with regard to the optical axis. On the other hand, there is known a composition for an astronomical telescope wherein an indication member with engraved lines in the plate-shaped transparent surface is arranged on a focusing member and illuminated with a light source arranged on one side of the outer circumference of said focusing member. In this case, however, a sand-blasted outer circumference of said transparent member absorbs and scatters the illumination light, thereby degrading illumination efficiency.
Further, Japanese Patent Publication No. 46568/1981 discloses a composition wherein an image of said indication member is formed in the observation optical path so as to be overlapped with an image to be observed by using an illuminating light source, a projecting lens and a beam splitter. However, this composition has a defect that it makes the photographing illumination device complicated and larger.